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Step-scan Terahertz Time-Domain Magneto-Spectroscopy

We have implemented a novel approach for terahertz time-domain spectroscopy of magneto-optic phenomena in collaboration with the Fraunhofer Institute in Kaiserslautern [1]. Our set up is displayed in fig. 1. It is based on a portable periodic pulsed magnet that was inserted in a standard THz time-domain spectrometer at Kaiserslautern. The detector measures the wave form of picosecond transients electric field transmitted through a sample sitting in the magnet bore. Emitter and detector are photoconductive antennas activated by trains of femtosecond laser pulses gradually delayed one against the other. Particularly, at fixed delay times, the detector photocurrent reads the change of electric field wave form caused by the pulsed magnetic field applied periodically to the sample. After stepwise increments of the delay time, one finally retrieves from the stored data first time-domain spectra at fixed magnetic fields as shown in Fig. 2 and then frequency domain spectra. Such spectra are displayed in Fig. 3 for a bulk n-type GaAs sample in the frequency domain from 200 GHz to 2 THz and in the magnetic field range up to 6 T. Also shown are a simulation of the spectra based on the Drude model. This experiment paves the way to implement time-domain spectroscopy measurements at high DC and pulsed magnetic fields.

Fig. (1) Sketch of the THz time-domain magneto-spectrometer. (2) Change of the electric field wave form transmitted through the sample and measured at fixed delay times as a function of magnetic field swept vertically at fixed delay times. (3) Magneto-transmission spectra for a bulk n-type GaAs sample. The sample temperature is 110K. Simulation using the Drude model.

[1] D. Molter, G. Torosyan, G. Ballon, L. Drigo, R. Beigang, and J. Léotin, Step-scan time-domain terahertz magneto-spectroscopy, Opt. Express 20, 5993-6002 (2012)

Contacts : Jean Léotin, Michel Goiran